Gauges: update value instead of re-creating on render

Update the gauge (used for park and rides RTI) rather than re-creating them each time it's refreshed (~ every 10 seconds).

Problems:
* current gauge (justgage) only allows to refresh the value (and the maximum), NOT the title (see https://github.com/toorshia/justgage/issues/71) so we now have to handle it separately
* this is not the normal flow using render